The present invention relates to the field of electrooptic switches for switching beams of light.
It is known to employ liquid crystals (LC) in conjunction with optical waveguides for switching light. See, for example, U.S. Pat. No. 4,201,442 issued to McMahon and Soref. That patent is not directed to the use of ferroelectric liquid crystals and uses out-of-plane crossover of two channels. The optic axis of the LC molecules goes from an in plane ordering to an out-of-plane ordering when voltage is applied, in contrast with the LC molecular axis remaining in the plane of the LC for both switching states in accordance with the present invention. In this prior art patent, light is allowed to leak out of one channel and into a second vertically stacked channel by raising the cladding index, so that the difference between the cladding index of refraction and the core index approaches zero, and the resulting leaky out-of-plane coupling only allows partial switching in practice and the largest transfer of light may be fifty percent.
Thus there is a need for an electrooptic LC switch having an active length of about one mm. and an overall switch length of about 2-3 mm, capable of complete switching with 100% exchange of signals. The switch of the McMahon and Soref patent is non-interferometric in nature, in contrast with preferred embodiments of the present invention.
There is also a need for an LC switch that has a ten microsecond response in contrast with far slower prior art nematic LC switches, with 15 volt, low current switching signals, and which may be used to construct low-loss monolithic switching networks that can be scaled to 32.times.32 switches at a wavelength of operation range between 0.5-1.8 microns, and which may be end-fire coupled to couple them to optical fibers without the use of costly prisms. It is true that deflecting-mirror switches respond in the microsecond range, but it is difficult to scale such a switch to large sizes. Semiconductor and LiNbO.sub.3 switches respond in nanoseconds, but the fabrication technology is complicated and costly; hence the need for a simple, low cost, reliable technology that can be implemented in large switching arrays such as 32.times.32 arrays.